Many oil formations are known to exist in which the oil or liquid petroleum occupies the pore spaces in the upper portion of a permeable formation, and the water occupies the pore spaces in the lower portion of the same or a contiguous permeable formation. Water encountered in such aquifers underlying oil containing formations is ordinarily brine, having a density greater than 1 and frequently in the range of from 1.01 to 1.3, whereas the density of oil is in the range of 0.8 depending on the composition of the particular crude oil. Many crude oils are known which have higher specific gravities, but almost invariably the specific gravity of petroleum encountered in subterranean formations is less than the density of brines ordinarily associated with the petroleum formations. It is common practice to drill a producing well into such an oil formation to a point near the bottom of the oil-saturated interval, then to plug off the bottom of the well and to establish perforations through the well casing into the oil saturated formation through which fluid petroleum may flow, which permits it to be pumped or otherwise transported to the surface of the earth. In many formations, a number of conditions coexist which results in the establishment of a phenomena known as bottom water coning, in which the oil-water interface rearranges itself from a previous essentially horizontal configuration into a cone rising along the walls of the oil well. This cone shaped water saturated interval is formed as a result of pressure differentials created in the formation, which causes water to rise into the previously oil saturated portion of the permeable formation despite the density difference between oil and water which would ordinarily maintain the water at a lower level. This problem is so acute that in some instances the water-oil ratio rises to a value so high that further production of oil from the well is not commercially feasible. If the well is shut in and the pressure differentials created in the formation during the period of fluid production are allowed to equalize, some levelling of the oil water interface occurs, although the problem quickly reoccurs when production of oil from the well is resumed.
Many methods have been proposed in the prior art for treating a well afflicted with bottom water coning so as to reduce or eliminate the tendency for water to rise along the walls of a producing well resulting in the production of an ever increasing fraction of water from the well. One method has been disclosed by the Applicant himself in U.S. Pat. No. 4,475,593, which discloses a method for profile control in subterranean formation structures by the formation of a barrier at some desired distance remote from the well bore. This unique process can be utilized to selectively exclude water from water producing intervals interspersed with the oil producing intervals, but it has not always been entirely satisfactory when used as a remedial method for treating a well experiencing bottom water coning. It is believed that the reason that the method has not always been entirely satisfactory when applied to a well experiencing bottom water coning is related to with the fact that the treating fluid injected into the formation in accordance with the method described in U.S. Pat. No. 4,475,593 has a density about equal to the density of the brine normally encountered in aquafers underlying oil saturated intervals, which forms the water cone around the producing well. Thus the injected treating fluid moves essentially horizontally out from the well and forms a "doughnut" shaped area around the well. Moreover, since the process of the method described in U.S. Pat. No. 4,475,593 is especially aimed at curing a problem of water production from water producing intervals interspersed with oil containing intervals, the process has been designed to favor forming the flow restraining barrier in the water saturated zone. Thus when the process is applied to a well experiencing bottom water coning, the barrier is formed essentially opposite the perforations of the well and in the zone which has been saturated with water or oil field brine as a consequence of coning phenomenon itself. If the treating fluid is displaced horizontally from the well perforations beyond the water cone zone, it is in an oil saturated interval and no reaction occurs to form the barrier.
Although many of the prior art methods proposed for treating wells afflicted with bottom water coning have been at least partly successful in some applications, the problem still remains one which is frequently encountered in the industry and produces serious economic consequences in certain formations including the necessity to abandon an otherwise productive oil well. Accordingly, there is a substantial unfulfilled need for a method which is especially suitable for treating wells in which the production of oil is declining and the production of water is increasing as a consequence of bottom water coning.